The key questions are :
How many rounds were discharged by police ?
What was the calibre of police rounds ?
How many bikers were killed by what calibre rounds ?
How many bikers were killed by what calibre biker rounds ?
How many bikers wounded by what calibre rounds ?
What calibre rounds were found on bikers in the 'threat zone' ?
How many police wounded by what calibre rounds ?
By their advance preparation (pole cam, on scene in advance), the police demonstrate having advance notice that THIS DAY and THIS PLACE was going to be hot. They knew the Cossacks were planning to "crash the meeting."
So, what did they do? They waited in their cars, just out of sight, and made sure that none of their people were inside the restaurant. They avoided confrontation, until it was too late.
I do understand that instigation and awareness are not the same thing, and my suspicion is that the cops played both parts, although I wrote here mostly of the awareness angle.